NOTOPTERNA: UN NUEVO ORDEN DE MAMIFEROS UNGULADOS EOGENOS DE AMERICA DE SUR. PARTE II. NOTONYCHOPS POWELLI GEN. ET SP. NOV. (NOTONYCHOPIDAE NOV.) DE LA FORMACION RIO LORO (PALEOCENO MEDIO), PROVINCIA DE TUCUMAN, ARGENTINA

Abstract

In this paper (part Il) the foundation of the Notopterna is completed with the description of Notonychops powelli gen. et sp. nov., from the lower part of the Rio Loro Fm. (referred to the "subage" Early Riochican; Middle Paleocene). N. powelli bears close resemblance to primitive tillodonts such as species of Esthonyx. Its characters are as follows: P11 absent; P2-4 with strong parastyle and metastyle and with paracone and protocone; M1-3 with a very strong parstyle; M3 lack hipoconid; P2-4 lack paraconid; M1-3 selenodont, bicrescentic, resembling those of the Indalecidae and primitive tillodonts. In considering its relationships, assignment to the Tillodontiais rejected on the basis of morphology, phylogeny and paleobiogeography. N. powelli is more closely related to the Indalecidae (Notopterna) and possibly has an ancestor among the Amilnedwardsidae (primitive Notoptema described in Part I). A new family, Notonychopidae, is proposed for this new adaptive type of Tertiary mammal from South America, Thus, the order Notopterna is considered to contain three families.